1. Field of Invention
This invention relates generally to a shunting system for treatment of hydrocephalus, and more specifically to an implantable micro-system for the treatment of hydrocephalus.
2. Description of Related Art
In order to better understand the prior art for treating hydrocephalus as well as the unique implantable micro-system of the present invention, the following brief discussion of the mechanism responsible for hydrocephalus should be helpful; although not necessary for a person skilled in the art.
Cerebrospinal fluid (CSF) is a water-like fluid produced in the brain that circulates around and protects the brain and spinal cord, as is well known to those skilled in the art. It is believed that CSF is absorbed into the superior sagittal sinus, a venous structure that drains blood from the brain, through biologic one-way valves referred to as arachnoid villi or granulations, which pierce the dura mater. The arachnoid granulations are exposed to cerebral spinal fluid that resides in the subarachnoid space on the basal side and with the venous blood of the superior sagittal sinus on the apical side. Hydrocephalus is an abnormal accumulation of CSF within the subarachnoid space of the brain due to impaired CSF absorption. As is known, the subarachnoid area is the region around the brain and is bounded by dura mater. The dura mater comprises the walls of the superior sagittal sinus.
Hydrocephalus is one of the most frequently encountered problems in neurosurgery. One of the most common methods of treating hydrocephalus is through a surgical procedure in which a tube, referred to as a “shunt,” is placed into the patient's body. The shunt system for diverting CSF from the intracranial compartment was developed in the 1950's, and has remained virtually unchanged for the past 50 years.
Essentially, the prior art shunts are implanted in a human body to channel the flow of CSF away from the brain into another part of the body. These prior art shunt devices generally include a single tube provided by a proximal catheter within the ventricular space and a distal draining catheter located within an absorptive surface of the body. Between the proximal and distal ends catheters is an intervening one-way valve device that is placed subcutaneously outside of the skull to limit the flow of CSF in one direction, i.e., away from the brain and direct the flow into the absorptive surface through the distal draining catheter. The most common absorptive surface employed in the prior art is the peritoneum of the abdominal cavity. This type of shunt system is referred to as a ventriculo-peritoneal (VP) shunt. Although VP shunts have operated successfully to prevent death and disability resulting from hydrocephalus, they do have a number of shortcomings.
The first major shortcoming of the current VP shunt is its high failure rate. In fact, it has been reported in the medical literature in 1998 that approximately 40% of the VP shunts failed after one year and approximately 50% failed after two years. Moreover, it is estimated that 50% of mechanical shunt failure is due to shunt blockage, which is usually highest in the immediate post operative period. Specifically, the proximal catheter can become occluded if the brain debris or parts of choroid plexus become attached to the pores of the proximal catheter resulting in diminished flow. The valve between the proximal and distal catheters also may become occluded by debris, blood clot or infection. Bacterial infections in the blood can seed the long course of the shunt tubing from the head to the abdomen resulting in failure. Other causes of failure include tubing breakage, kinking or shortening due to patient growth or movement. All of the above-mentioned factors result in the published failure rate set forth above. As can be envisioned, this high failure rate results in frequent patient visits to the Emergency Room, frequent diagnostic procedures, hospitalizations and repeat surgery for shunt revisions. In addition to the high failure rate of prior art shunts posing a potentially dangerous situation for the patient, the high failure rate also results in increased health care costs. While the economic costs are believed to be enormous, the human cost of multiple hospital visits and surgical procedures, especially in the pediatric population simply cannot be measured.
An additional problem encountered with current VP shunts is the imprecise flow of CSF, e.g., over- or under-shunting. Under-shunting occurs when CSF is not evacuated from the brain fast enough to maintain equilibrium with its production within the brain. In this situation, the VP shunt has not adequately treated the hydrocephalus. The limitations of valve design as well as some partial occlusion can produce this under-shunting. Over-shunting is also a limitation of the current shunt design, in which too much flow is allowed through the valve to thereby create an undesired lower than normal pressure around the brain. Such a low pressure usually is exacerbated by changes in a patient's posture from a recumbent to an erect position. In addition, a siphon effect can additionally lead to problems of over-drainage.
In an attempt to solve problems of imprecise shunting programmable valves (electromagnetically adjustable) have been commercialized. One supplier of such valves is Cordis. These programmable valves permit neurosurgeons to pre-select one of multiple pressure settings of the valve at the time of implantation. After implantation, the valve can be adjusted non-invasively using a magnetic device to individualize the flow rate to a particular patient's situation. This means that surgeons are able to make adjustments to help control intracranial pressure as a function of CSF elimination. However, the actual intracranial pressure cannot be monitored after implantation. and a change in pressure setting will be variable based on whether the patient is erect or recumbent. Also, it has been reported in the literature that household magnets can change the programmable shunt valves, thereby resulting in a failure of the shunting system. Thus, the use of electromagnetically adjustable, programmable shunting valves has not proven to be a great advantage, and still being prone to other problems, such as shunt failure, breakage, clogging, and infection. Moreover, these valves do not adapt to changing patient positions once having been set.
Anti-siphon devices also have been employed to correct problems of over shunting due to changes in patient position. As reported in the medical literature, this also has not alleviated the problems associated with imprecise flow.
Recently, e.g., approximately 2004, an active shunt system was proposed, which consisted of a micro telemetry pressure sensor, a micro pump, and a controller. In this system, the controller controls the micro pump according to the intracranial pressure created by the CSF and measured with the telemetry pressure sensor. It is Applicant's understanding that pressure sensor and micro pump prototypes have been tested in-vitro. Although this particular approach could possibly provide an active form of moving CSF in relation to instantly measured pressure gradients, and also might be useful in monitoring the intracranial pressure after implantation for diagnostic purposes, there are still many obstacles to overcome with this later proposed system, e.g., power supply, complex circuitry, multiple moving parts, as well as the earlier mentioned problems of the current systems; namely, breakage, clogging, infection and the use of only a single outlet.
The following patents disclose prior art systems for the treatment of hydrocephalus:
U.S. Pat. No. 4,432,853BanksU.S. Pat. No. 5,897,528SchultzU.S. Pat. No. 6,027,863Donadio, IIIU.S. Pat. No. 6,030,358OdlandU.S. Pat. No. 6,107,004Donadio, IIIU.S. Pat. No. 6,589,198Soltanpour et al.U.S. Pat. No. 6,913,589DextradeurU.S. Pat. No. 7,037,288Rosenberg et alU.S. Pat. No. 7,118,548Børgesen
The present invention is believed to have the capability of overcoming virtually all of the problems associated with the prior art shunting systems, as described above.